1. Field of the Invention
The present invention relates to a bearing arrangement, particularly but not exclusively in the field of precision bearings for example for measurement apparatus having articulated wrist parts.
2. Description of Related Art
Precision bearings of many forms are known. The simplest rely on the sliding contact to transfer loadings. More complicated bearings have rolling contact, for example ball race or roller sets. Rolling contact is preferred for high loadings, high rotational speeds and long bearing life. However these bearings need to be manufactured in an accurate manner and are consequently expensive. Where thin section parts are used they tend to take up the shape of the housing to which they are fitted. As a consequence, their housings too must be accurately made if good accuracy of movement is to be maintained.
Sliding contact bearings may be used for precision bearings, for example watch bearings. Watch bearings, and similar, are lightly loaded and so do not need large bearing surfaces to transfer forces. Typically a rotatable shaft might have conical ends and be held in place between two plates with complementary end accepting parts. This type of bearing, although simple and low cost, is difficult to adjust when wear takes place. Wear being more common where sliding contact is employed.
One commercially available bearing, used typically for roundness measurement machines provides a fixed block, e.g. of P.T.F.E., having a conical recess and a ball seated rotatably within the recess. Again wear adjustment for such a bearing is problematic and the arrangement is not used in pairs.